SUMMARY

In Atlantic bottlenose dolphins Tursiops truncatus, both the
thickness and lipid content of blubber vary across ontogeny and across
individuals of differing reproductive and nutritional status. This study
investigates how these changes in blubber morphology and composition influence
its thermal properties. Thermal conductivity (W m–1
deg.–1, where deg. is °C) and thermal insulation
(m2 deg. W–1) of dolphin blubber were measured in
individuals across an ontogenetic series (fetus through adult, N=36),
pregnant females (N=4) and emaciated animals (N=5). These
thermal properties were determined by the simultaneous use of two common
experimental approaches, the heat flux disc method and the standard material
method. Thickness, lipid and water content were measured for each blubber
sample. Thermal conductivity and insulation varied significantly across
ontogeny. Blubber from fetuses through sub-adults was less conductive
(range=0.11–0.13±0.02 W m–1
deg.–1) than that of adults (mean=0.18 W m–1
deg.–1). The conductivity of blubber from pregnant females
was similar to non-adult categories, while that of emaciated animals was
significantly higher (0.24 ± 0.04 W m deg.–1) than all
other categories. Blubber from sub-adults and pregnant females had the highest
insulation values while fetuses and emaciated animals had the lowest. In
nutritionally dependant life history categories, changes in blubber's thermal
insulation were characterized by stable blubber quality (i.e. conductivity)
and increased blubber quantity (i.e. thickness). In nutritionally independent
animals, blubber quantity remained stable while blubber quality varied. A
final, unexpected observation was that heat flux measurements at the deep
blubber surface were significantly higher than that at the superficial
surface, a pattern not observed in control materials. This apparent ability to
absorb heat, coupled with blubber's fatty acid composition, suggest that
dolphin integument may function as a phase change material.